The present invention relates to a scintillation camera, and more particularly relates to the mechanical structure of such a camera. In its most immediate sense, the invention relates to apparatus which adapts the camera for attachment of a collimator.
A conventional scintillation camera such as a gamma camera includes a detector which converts into electrical signals gamma rays emitted from a patient after a radioisotope has been administered to the patient. The detector includes a scintillator and photodetectors. The gamma rays are directed to the scintillator (usually a crystal of thallium-doped sodium iodide) which absorbs the radiation and produces, in response, a minute flash of light. An array of photodetectors, which are placed in optical communication with the scintillation crystal, converts these flashes to electrical signals which are subsequently processed. After processing, the camera produces an image of that region of the patient from which the radiation was emitted.
Since the gamma radiation is emitted in all directions, it is necessary to collimate the radiation before the radiation is made incident upon the scintillation crystal. This is accomplished by using a collimator, which is a lead body perforated by relatively narrow channels. The collimator is detachably secured to the detector head, permitting the collimator to be changed so that, for example, the same camera can be used with different radioisotopes or different collimation patterns. A collimator may be quite massive, especially where it is intended for use with high-energy radioisotopes.
Where the gamma camera is used in SPECT (single photon emission computed tomography) to produce a three dimensional image of an organ being imaged, the detector is conventionally rotated about the patient. The detector is also moved when positioning it to reach a fixed position to produce a planar image. In both instances, it is conventionally necessary to counterbalance the detector so that the rotation/movement does not place excessive loads on the drive motors which are used to move the detector.
To avoid repeated rebalancing when substituting one collimator for another one of different weight, it is possible to equalize the weights of all collimators. Although this may optimize the balance of the scintillation camera, this optimization is achieved at the expense of image quality since the collimators cannot be optimized and the collimator is an important factor in image quality.
In a known scintillation camera manufactured by General Electric, the camera has a movable counterweight which can be moved by rotating a manually-operable crank. Such manual adjustment of the counterweight is, however, insufficient to attain precise balance, and also restricts the weight range of collimators which can be attached to the detector, since the counterweight can only be adjusted within relatively narrow limits.
It is also possible to use more powerful drive motors and sturdier drive mechanisms to avoid the need for adjustable counterbalancing of the detector. This has the disadvantage that the detector cannot be moved by hand. Such manual positioning of the detector is desirable as it permits more rapid and precise handling.
It is thus a general object of the present invention to provide an improved scintillation camera which does not suffer from these drawbacks.
One object of the invention is to provide a scintillation camera which places few constraints on the design of collimators which are to be used with it, thereby permitting the collimator design to be further optimized and providing improved results.
Another object is to provide a scintillation camera which can be manually moved even though it may be attached to collimators of widely different weights.
Still a further object is to provide a scintillation camera which will automatically counterbalance its gantry when the collimator is changed.
Yet another object is, in general, to improve upon known scintillation cameras.
In accordance with the invention, a scintillation camera with a gantry and a detector secured to the gantry has means for counterbalancing the gantry. Means are provided to detachably secure a collimator to the detector. The camera also has means for identifying the collimator which is so secured. A control means is connected to the identifying means and the counterbalancing means. The counterbalancing means is automatically adjusted so as to appropriately counterbalance the gantry in accordance with the collimator which is secured to the detector.
In further accordance with the invention, the counterbalancing means counterbalances the gantry with respect to two axes. Advantageously, one axis passes through the detector, and the other axis is parallel thereto.
In still further accordance with the invention, the gantry permits the detector to be rotated and is counterbalanced with respect to the axis of rotation. Thus, in the preferred embodiment, the gantry is counterbalanced with respect to three axes.
In preferred embodiments, the collimators which are designed for use in accordance with the invention are encoded using magnets, and Hall sensors in the detector head respond to the presence and absence of magnets to cause the counterbalancing mechanism in the camera to be appropriately adjusted.
Because there is an automatic readjustment of the camera gantry, the collimators which are designed for use with the camera are not constrained to fit within a narrow weight range. Also, the automatic readjustment of the gantry in response to the actual weight of the attached collimator makes it possible to so accurately counterbalance the camera that it can be easily moved by hand.